1. Field of the Invention
The present invention relates to a solid electrolytic capacitor formed by mounting a capacitor element on an insulating substrate.
2. Description of Related Art
In a conventional solid electrolytic capacitor, as shown in FIG. 16, a capacitor element 101 is coated with an enclosure resin 102. Inside the enclosure resin 102, one end part 103a of an anode terminal 103 is connected to an anode section 101a of the capacitor element 101, while one end part 104a of a cathode terminal 104 is connected to a cathode section 101b of the capacitor element 101. Both the anode terminal 103 and the cathode terminal 104 are drawn out from the enclosure resin 102, and are bent along an outer peripheral surface of the enclosure resin 102 so that the other end parts 103b, 104b of the terminals 103, 104 are located along a lower surface 102a of the enclosure resin 102. The end parts 103b, 104b of both the terminals 103, 104 located along the lower surface 102a of the enclosure resin 102 form lower surface electrodes of the solid electrolytic capacitor.
In a manufacturing process of the solid electrolytic capacitor described above, required is a complicated step of bending the anode terminal 103 and the cathode terminal 104. In addition, since the enclosure resin 102 of appropriate thickness needs to be interposed between a lower surface of the capacitor element 101 and the lower surface electrodes, there has been a problem of lower occupancy of the capacitor element 101 in the solid electrolytic capacitor, or a problem of greater equivalent series resistance (ESR) or equivalent series inductance (ESL) due to an increase in lengths of the anode terminal 103 and the cathode terminal 104.
Therefore, as shown in FIG. 17, it has been proposed to form the solid electrolytic capacitor by mounting the capacitor element 101 on an insulating substrate 107 (e.g., a printed board) in which an anode terminal 105 and a cathode terminal 106 are formed.
In the solid electrolytic capacitor shown in FIG. 17, the anode terminal 105 comprises a first anode section 105a formed on an upper surface 107a of the insulating substrate 107 and a second anode section 105b formed on a lower surface 107b of the insulating substrate 107, which are electrically connected to each other by an anode conductive layer 105d. The anode conductive layer 105d is formed by plating an inner surface of an anode via 105c opening in the insulating substrate 107.
Also, the cathode terminal 106 comprises a first cathode section 106a formed on the upper surface 107a of the insulating substrate 107 and a second cathode section 106b formed on the lower surface 107b of the insulating substrate 107, which are electrically connected to each other by a cathode conductive layer 106d. The cathode conductive layer 106d is formed by plating an inner surface of a cathode via 106c opening in the insulating substrate 107.
Further, in the solid electrolytic capacitor shown in FIG. 17, to the first anode section 105a, electrically connected is the anode section 101a of the capacitor element 101 through a pad member 108, while, to the first cathode section 106a, electrically connected is the cathode section 101b of the capacitor element 101 by a conductive adhesive. The second anode section 105b and the second cathode section 106b form the lower surface electrodes of the solid electrolytic capacitor.
Thus, by using the insulating substrate 107 to form the solid electrolytic capacitor, a distance from the lower surface of the capacitor element 101 to the lower surface electrodes decreases. Therefore, lengths of the anode terminal 105 and the cathode terminal 106 decrease, resulting in reducing the ESR or ESL. Moreover, due to the employment of the insulating substrate 107 in which the anode terminal 105 and the cathode terminal 106 are formed, it is not necessary to execute the complicated step of bending the anode terminal and the cathode terminal required in the manufacturing process of the solid electrolytic capacitor shown in FIG. 16.
In order to further reduce the ESR or ESL in the conventional solid electrolytic capacitor shown in FIG. 17, there is an idea to mount a plurality of capacitor elements 101 on the insulating substrate 107 to thereby increase total connection area between the anode sections 101a of the capacitor elements 101 and the first anode section 105a of the anode terminal 105, as shown in FIG. 18.
However, in the conventional solid electrolytic capacitor shown in FIG. 18, the second anode section 105b and the second cathode section 106b which are to be the lower surface electrodes are arranged so as to be spaced from each other in a length direction 191 of the solid electrolytic capacitor, and the first anode section 105a and first cathode section 106a are also arranged so as to be spaced from each other in the length direction 191. Therefore, in the conventional solid electrolytic capacitor, it has been necessary that the plurality of capacitor elements 101 are aligned in a width direction 192 of the solid electrolytic capacitor, and that each of the capacitor elements 101 is connected to the first anode section 105a and the first cathode section 106a, with the anode section 101a being oriented in the length direction 191.
Because of this, in the case where the number of capacitor elements 101 to be mounted is increased in order to increase the total connection area, if the capacitor elements 101 of the same size are used, the width of the solid electrolytic capacitor increases, and the size of the solid electrolytic capacitor is changed. In the case of such a size change, a position of a land on a wiring board to which the solid electrolytic capacitor is to be connected should be changed with the size change.
On the other hand, there is an idea of designing the capacitor element 101 to be long and thin in order to increase the number of capacitor elements 101 to be mounted without changing the size of the solid electrolytic capacitor. However, with such a structure, a thickness of an anode body 101c (cf. FIG. 17) (a distance from an outer peripheral surface of the anode body 101c to the anode lead 101d) decreases, and a crack may disadvantageously be generated in the anode body 101c during sintering. Also, a position shift of the capacitor element 101 occurs easily at the time of mounting the capacitor elements 101 on the insulating substrate 107, and this makes the mounting of the capacitor elements 101 on the insulating substrate 107 difficult.